We’ve already told you to consider eating more marsh rodents for the sake of the environment. Now, we’re begging you to stop releasing pet goldfish into local waterways. The seemingly benign and tiny household pets can grow to gargantuan sizes, like the ones the United States Fish & Wildlife found during a recent survey of Presque Isle on Lake Erie.
“This goldfish isn’t supposed to be here. But someone released it, thinking they were being kind. Instead, they created an invasive problem that can last decades,” the agency wrote on Facebook.
When released into the wild, goldfish can harm the water quality in only two years. They can uproot plants, contribute to harmful algal blooms, and eat vegetation in environmentally and economically sensitive regions like the Great Lakes.
“Many of the reasons that make goldfish invasive upon release are the same reasons that they make great pets and pet trade species,” Sara Ricklefs, Executive Director of the Invasive Species Action Network, tells Popular Science. “They are generalists so they don’t have many dietary or habitat restrictions. They’re a hardy fish and able to persist in the environment (withstanding a range of water temperatures and water quality factors).”
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Their “bottomless appetites” help them grow incredibly quickly and they will steal food from native fish and harm their reproduction. The Ohio State University College of Food, Agricultural, and Environmental Sciences, says that invasive goldfish will eat the eggs of native fish species and take over the critical habitats that other fish use for reproduction and shelter. The goldfish will also reproduce with the native common carp to create bigger hybrid species that are equally harmful.
The problem has been very pronounced in the Great Lakes between the United States and Canada. A 2023 study published in the Journal of Great Lakes Research described an invasive population of goldfish in Lake Ontario’s Hamilton Harbour, southwest of Toronto. Between June 2017 and October 2018, the authors captured 19 adult goldfish and implanted transmitters in the fish that they used to track where the goldfish swam.
The team used this data to build models that accurately anticipated the arrival of the tagged fish. The goldfish move into their spawning grounds when temperatures hit about 50 degrees Fahrenheit and understanding this movement can help environmental officials pinpoint regions for culling. Some of the options for catching the goldfish include using nets beneath winter ice, shocking them with electrical currents, or scooping them out of the water.
[ Related: How goldfish use booze to get through a hard winter. ]
If you can no longer care for a live goldfish, the United States Fish & Wildlife Service recommends trying to find another caregiver, donating a fish to an aquarium or school, returning it to a pet store, and checking online forums and social media dedicated to pet adoption.
The Invasive Species Action Network also has fish rehoming resources and urges potential pet owners to consider local and state regulations when choosing a pet fish as well as the vegetation planted around them.
“Releasing a pet is never the answer. If you have an aquarium, take care when choosing aquatic plants, as well. Aquatic plants can also be highly invasive,” Ricklefs explains. “If you have plants that you need to trim or remove from your pond or aquarium, throw them away in a sealed bag or rehome them too.”
